This invention relates to electromagnetic relays and contactors, and is more specifically related to the structure of an electromagnetic or electromechanical relay of the type that has a winding or coil that is energized to move an armature such that a load current may be applied to a load device. Relays and contactors may be considered as devices in which the appearance of a pilot current or voltage causes the opening or closing of a controlled switching device to apply or discontinue application of load current. The invention is particularly concerned with a combination of a relay and a current sensor for measuring the amount of load current, or the quality thereof, that is being applied to the load device.
Electromagnetic or electromechanical relays or contactors are devices in which current that flows through an actuator coil closes or opens a pair of electrical contacts. This may occur in a number of well-known ways, but usually an iron armature is magnetically deflected towards the core of the coil to make (or break) the controlled circuit. In electromechanical relays, the voltage drop across the switching or output contacts is low, i.e., on the order of millivolts, so any power loss through the relay contacts is kept low in comparison with solid state relays, where the forward voltage drop may be one volt or sometimes higher.
Electromagnetic or electromechanical relays are commonly used to control the application of power to a load, for example, to control the application power to a blower or fan in a ventilation, heating, or air conditioning system. These devices are inexpensive and in general have good reliability over a reasonable life span. Wear of the contacts may occur in time due to arcing if the relay acts to break the circuit at a time when there is significant current load flowing. This may also produce switching noise, which may disturb electronic devices located near the relay.
If it is desired to monitor the load current to the associated load device, a separate current sensor is employed. This may involve a hall-type solid-state device or other current detector device. This adds circuit complexity and cost to the control circuitry for the load device.